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Requirements Specification
Overview:
The design of an RFI-Mitigating Digital Radiometer Detector will result
in a prototyped subsystem of a microwave radiometer. The analog square-law detector and low-pass
filter used to measure signal power in a conventional radiometer are to be
replaced with high-speed digital signal processing. This will allow spectrally narrow radio
frequency interference to be removed before the signal power is measured.
Background:
Radio Frequency Interference (RFI) has become an increasing problem for
microwave remote sensing in Earth Science applications. Data from the AMSR-E
instrument shows widespread interference throughout much of the United
States, particularly in heavily
populated areas. [1] The ESTAR instrument shows significant spurious RFI from
air traffic control radar in the L-band spectral window set aside for passive
use. [2] These studies show that RFI is a major concern for microwave remote
sensing of the earth. Two L-band radiometer instruments, Aquarius and Hydros, are currently being developed at the NASA/Goddard
Space Flight Center. For both of these instruments, RFI is expected to be a
potential source of error or data-loss, particularly in the soil-moisture
data collected by Hydros.
Deliverables:
- One RFI-Mitigating Digital
Radiometer Detector prototype
- One Analog Test Signal
Generator
Operation Description:
The RFI-Mitigating Digital Radiometer Detector is a subsystem of a
radiometer. It will input the
amplified noise signal, and output the power.
In addition it will remove spectrally narrow radio frequency
interference.
Requirements Specification:
The prototype will…
- Measure the power of a
25MHz bandwidth input noise signal.
- Remove sinusoidal RFI
20 dB below the power of the input noise signal.
- Output the bandwidth
uncorrupted by RFI.
- Be tested at L-band
(Center frequency 1.413 GHz.
- Include a hardware
test interface which allows testing at several different input noise
powers.
Preliminary Test Plan:
Using the Analog Test Signal Generator, several different brightness
temperatures will be fed to the prototype.
The prototype must output the power of the signal. In addition, a sinusoid will be added to
the input signal. The prototype must
remove the corrupted sinusoid from the input signal and output the
uncorrupted power.
Works Cited:
- Li, L., E.G. Njoku, E. Im, P.S. Chang,
K. St. Germain, “A Preliminary Survey of
Radio-Frequency Interference Over the U.S. in Aqua AMSR-E Data,” IEEE
Trans. on Geoscience and Remote Sensing,
vol.42(2), pp. 380-390, 2004.
- Piepmeier,
J.R., M. Midon, A. Caroglanian,
O.C. Ugweje, “Radio frequency survey of
the 21-cm wavelength (1.4 GHz) allocation for passive microwave
observing,” Geoscience and
Remote Sensing Symposium, vol. 3, pp. 1739-1741, July 2003.
Updated 2005 September 28
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